Electrophotographic material



United States Patent 0 3,153,475 ELECTRGPHGTOGRAPHIC MATERIAL Paul Maria Cassiers, Jean Marie Nys, and Jozef Frans Wiilems, Martsel-Antwerp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsei, Eeigiuni, a Beigian company No Drawing. Filed Feb. 4, 1969, Ser. No. 6,625 Claims priority, application Great Britain Feb. 5, 1959 1 Claim. (Cl. 96-1) 3,158,475 Patented Nov. 24, 1964 anthracene, benzidine or a heterocyclic compound of a determined type.

Now we have found that electrophotographic material with particularly favorable properties and suitable to be used in the application of the most widely varying electrophotographic reproduction methods is obtained if in the manufacture of the photoconductive layer compounds are used having the general formula R- CH=CH-) ll wherein R and R each represent an aryl radical or a substituted aryl radical; n represents 1 or 2.

Some compounds according to the above formula which seemed to be particularly suitable for the manufacture or" the electrophotographic material according to the present invention are given hereinafter in Table 1.

TABLE 1 R n Prepared according to Org. Syntheses 23, 86.

N0 1 P. Pflelign and Scrgiewskaja Ber.

R. Stoermer and H. Ochlert Ber.

4---" H2N NHZ 1 K. Elbs and o. Hoermarm, J,

prakt. Chem. (2) 39, 502. o.N- G an 1 J.N.Ashleye.a.,I.C.S.1942, 112. 6 OQN C C NO, 1 P. Walden andA. Kcrnbaum, Ber.

(IJN OHa CH3 9 ON N 1 I. Pfeifier, Ber. 48, 1796.

orr

I i on. 10...- NCC -N/ 1 P. Pfeitter, Ann. Chem. 465, 46.

oH3 NH;

on 11. (MN-@- N 1 P. Pfeitler, Ber. 48,1808.

6N CH3 12 NC-Q- O-N 1 P. Pfeifler, Ber. 48, 1808.

N02 CH3 13---- mN-Q 6-01 1 14.- H2NAC -OCH3 1 P. Pfeifier, Ber. 48, 1794.

TABLE 1-Continued n Prepared according to- 1 P. Pl'eifler, Ben-48, 1793.

P. Ruggli and F. Lang Helv.

Chim. Acta 1936, 1004.

2 S. Israelashvili, J.. Org. Cherrnlfi,

2 S..-Israe1ashvlli, J. .Org. Chem. 16,

The compounds 3, and 14 are obtained by catalytic hydrogenation of the corresponding nitro derivatives in the presence of. Raney nickel.

The-compounds '7, '8 and '13 'are'likewise obtaine'd'by catalytic hydrogenation. For this purpose they are dissolved resp. in ethanol, methanol and ethylacetat'e. After the reaction the compounds 7 and 8 are recrystallized from hexane. Their melting points are resp. .85" and 190 C.

Compound 17 is obtained by heating 17.5 g. of

:p-dimethylaminocinnamic aldehyde, 16.2 g. of p-nitro-otolunitrile and 10 cm? of piperidine for 2 h. on an oil bath. After cooling, the reaction mixture is treated with Warm acetic acid. The solution thus obtained isfiltered and cooled off. The synthetic product crystallizes out in fine-black green-glossying needles. After recrystallization from acetic acid the melting point is 210 C.

For the manufacture of the electrophotographic material according to the present invention, a photoconductive layer containing at least one of the compounds according to the above general formula or mainly consisting of at least one of the compounds according to the above general formula is applied to a suitable support.

The photoconductive layers according to the present invention can contain besides one or more of the compounds according to the above general formula still-one or more other photoconductive compounds with similar or difierent photoelectric-, mechanicalor other physical properties; moreover, there'can be present in the photoconductive layer other compounds which confer the properties desired to the photoconductive layer and/or'tothe composition wherefrom this layer is formed.

Thus, in the manufacture of the photoconductive layers according to the present invention one or more macro molecular compounds can be added as binding'agents to the composition wherefrom the photoconductive layer is formed; preferably, macromolecular compounds with high specific resistivity (i.e. with a specific resistivity higher than 10 ohm.-cm.) are used for this purpose; macromolecular compounds particularly suitable as binding agent for the photoconductive layers are-e.-g. natural resins, such as darnmar resin, elemi-resins, gum arabic, manila gum and sandarac resin; micro-crystalline waxes; modified natural substancessuch as cellulose diacetate and cellulose triacetate, cellulose acetobutyrat'e, ethyl cellulose, ethyl cellulose stearate or other cellulose derivatives pentaerythrite polyesters or other modified colophonium resins and ester gums; polymerisatessuch as polyethylene, polystyrene and copolymers of styrene, polyvinylacetate and copolymers of vinylacetate, polyvinylacetals of formaldehyde, acetaldehyde, butyralde- .dimethylphthalate,

the layers.

hyde, polyacrylic acid esters and polymethacrylic acid esters and coumarone indeneresins;and polycondensates such as glycerol-phthalate resins and other glyceryl polyesters, alkydreshis polyethylene glycolesters, diethylene glycol polyesters, formaldehyde resins and silicone resins;

particularly good results \can be attained by using the polyesters described in US. patent application Serial No. 702,252, filed December 12,1957, and polysulphonates such as described in-lU.S.patent application Serial No. 797,587, filed March 3, 1959.

In the choice of -.a suitable binding-agent one is not limited to previously polymerized compounds; indeed, also low molecular compounds .can be used or mixtures of -1low and high molecular compounds, or semi-polymerisates which are polymerized in condensed in situ or undergo cross-linking according to one of the methods known in polymer chemistry.

If desired, suitableplasticizers such as dibutylphthalate, dimethylglycolphthalate, tricresylphosphate, triphenylphosphate, monocresyldiphenylphosphate, etc., in quantities -amounting to 10 to 30% by weight of the amount of bindingagentused can be added to the compositions forthe formation of the photoconductive layers containing a binding agent.

Further can still be-used other additives well known in the coating technique such'as for instance pigments, compounds which influence the gloss and/or the resistivity, compounds which counteract the aging and/ or the oxidation or whichiniluence the thermal stability of In thevchoice of 'these additives, those are preferred which do notreduce or only slightly reduce the: dark-resistivity of the photoconductive layer.

The thickness of thelayers is not critically established .but is determinedby the requirement of each separate case. Good results are attained with electrophotographic layers the thickness of which varies between 1 and 20 1. and preferably between 3 and 10p, for layers which are too thin possess anlinsuflicient insulating power whereas layers which are too'thickrequire long exposure times.

Finally, accordlingsto the presentiinvention compounds which either, do or do not possess photoconductive properties and which cause an increase of the general sensitivity and/or of the-sensitivity to electromagnetic rays from a determined par-tot the spectrum can also be present in the photoconductive layers.

Suitable compounds for increasing .the general sensitivity and/or the sensitivity to electromagnetic rays from the visible part of the-spectrum are e.g. those which for (that purpose are described inthe copending application Serial No. 6,627 for Electrophotographic Material filed on even date herewith.

In the manufacture of the electrophotographic material according to the present invention is preferably used as support for the photoconductive layenan electrically conductive plate or sheet, or an insulating plate or sheet provided with an electrically conductive layer. Under electrically conductive plate, sheet or layer is understood a plate, sheet or layer the specific resistivity of which is smaller than that of the photoconductive layer, i.e. in general smaller than ohm-cm. Supports the specific resistivity of which is less than 10 ohm.-cm. are preferably used.

Suitable insulating plates are e.g. glass plates; these plates must be coated with a conductive layer, e.g. with a transparent layer of silver, gold or stannous oxide deposited thereon e.g. by vacuum evaporation.

Suitable insulating sheets are for instance films of synthetic macromolecular substances with high specific resistivity such as for instance the polysulphonates described and claimed in the copending patent application Serial No. 797,587, for Production of Linear Aromatic Polyesters, filed March 6, 1959; polyesters such as those described and claimed in the copending patent application Serial No. 702,252, for Production of Linear Aromatic Polyesters, filed December 12, 1957; Serial No. 725,498, for Production of Linear Aromatic Polyesters, filed April 1, 1958; Serial No. 731,874 for Production of Linear Aromatic Polyesters, filed April 30, 1958, polystyrene, polyethylene, cellulose esters etc. or sheets of paper with high specific resistivity. The insulating sheets must be provided with a conductive layer e.g. a thin metal sheet, with a layer comprising a metal powder dispersed in the smallest possible amount of binding agent, or with a thin hydrophilic layer comprising a hygroscopic and/or antistatic compound and a hydrophilic binding agent. Suitable hygroscopic and/ or antistatic compounds are for instance glycerine, glycol, polyethylene glycols, calcium chloride, sodium acetate, condensation products of maleic acid and polyethylene glycols,.cit ric acid amides, hydroxypro-pyl sucrosemonolaurate, quaternary ammonium compounds, amine salts of lyophilic alkylphosphates, lyophilic dialkylpolyoxyalkylene phosphates and polyoXyalkylene-am-ides. able hydrophilic binding agents are for instance gelatin, glue, polyvinyl alcohol, methylcellulose, carboxymethylcelluiose, cellulosesuphate, cellulose hydrogen phthalate, cellulose-acetatesulphate, hydroxyethyl cellulose, polyacryiic acid or colloidal silica; for obtaining a good adhesion of the hydrophilic layer and the hydrophobic polymeric sheet, the polymeric sheet can be provided with a suitable subbing layer such [as for instance one of the subbing layers described in the copending patent application Serial No. 509,333, for Manufacture of Photographic Film, filed May 18, 195 5 (for polyester films), the British Patent 819,592, the copending .patent application Serial No. 826,129, for Subbing Method for Polyalkylene Materials, filed July 10, 1959, and the Belgian Patent No. 569,129 (for polyalkylene films), US. Patent 2,867,542 (for cellulose ester films) and the Belgian Patent No. 573,055 (for hydrophilic layers with polyvinyl alcohol as binding agent).

Suitable conductive plates are for instance plates of metals such as aluminum, zinc, copper, tin, iron or lead.

Suitable conductive sheets are for instance films made of polymeric substances with low specific resistivity such as for instance polyamide films or paper sheets with low specific resistivity. Good results can be attained by using paper sheets containing hygroscopic and/or antistatic substances as described above. These hygroscopic and antistatic substances are preferably incorporated into the paper sheets during the paper manufacturing process either by adding them to the paper pulp or by an aftertreatment, before or after calendering the paper sheets.

Suit- 6 These substances can likewise be incorporated into the paper sheets by applying to the raw paper stock a composition containing the hygroscopic and/or the antistatic substances and a hydrophilic binding agent as described above.

For attaining optimal results it has been stated that paper sheets with a weight of 3060 g. sq.m. are most suitable.

It was likewise stated that particularly good results are attained when using paper sheets provided with a coating of a polymeric substance in order to obtain a smooth surface and to prevent the organic liquid wherein the photoconductive substance is dissolved from penetrating within the paper sheet. This coating, however, must not prevent the carrying-01f of the electrons from the exposed image areas during the irradiation. Suitable coatings are for in stance coatings with a thickness of 2 to 10 and composed of one or more of the macromolecular compounds described above as binding agent for the photoconductive compound.

Besides the usual paper sorts can likewise be used synthetic paper sorts such as those prepared from polyesters fibers from terephthalic acid and gly'cols from polyamide fibers or nylon-fibers or from polyacrylonitrile fibers. Before coating the photoconductive layers on such paper sheets, the latter are preferably impregnated with substances enhancing their conductivity, for instance polycaprolactam, the polyester of 1-chloro-3-aminobenzene- 4,6-disulphochloride, a copolyamide of hexamethylenediamine, caprolactam, adipic acid and sebacic acid, N-methylene polyhexamethylene adipamide adipamine or polyamides.

For the preparation of the elec'trophotographic material according to the present' invention various techniques can be applied when coating the support with a photoconductive layer.

In practice, the compounds acording to the above general formula either alone or together with other additives such as for instance binding agents, compounds which enhance the sensitivity etc. are preferably first dissolved or dispersed in a suitable organic solvent such as for instance benzene, acetone, methylene chloride, dioxane, dimethylformamide or glycol monomethyl-ether, or in a mixture of two or more 'of such solvents. The solution or dispersion thus obtained is uniformly spread on a surface of a suitable support, for instance by centrifuging, spraying, brushing or coating whereafter the layer formed is dried in such a way that a uniform photoconductive layer is formed on the surface of the support.

A particularly interesting method for applying to a support a photoconductive layer containing little or no binding agent is as follows: a solution of the photoconductive substance is applied to the support in such a way that a micro-crystalline layer is formed; for this purpose, is preferably used a heated, strongly concentrated solution of the photoconductor in a strong organic solvent and the layer formed is preferably quickly dried for instance in a hot air current or by action of infrared radiation.

Electrophotographic materials according to the present invention can be used in any of the different techniques whatever, which are based on the exposure and the discharge of an electrostatic charge provided in or on a photoconductive layer. 1

The electrostatic charging of the according to the present invention can be effected according to one of the methods known in electrophotography, for instance by friction with a smooth material, by friction with a material possessing a high electric resistivity such as for instance a cylinder coated with polystyrene, by corona discharge, by contact charge or by discharge of a capacitor.

The electrophotographic material is thereafter imagewise exposed to a suitable electromagnetic radiation whereby the radiated parts of the layer are image-wise disphotoconductive layer charged and an electrophotographiclatent image is obtained. The electrostatic latent image formed is then converted into a visible image either on theelectrophotographic material whereon the latent image was formed, or

on a material onto which the electrostatic latent image was transferred for instance by application of the method as described in the Belgian Patent No. 529,234.

The conversion of the original or transferred latent image into a visible image can occur according to one of the techniques known in electrophotography wherein use is made of the electrostatic attraction or repulsion of finely divided colored substances which for instance are present in a powder or powder mixture, in an electric insulating liquid (for instance in the form of suspension) or in a gas (for instance in the form of aerosol), or of finely divided colored liquid drops which are for instance present in an electrically insulating liquid (for instance in the form of dispersion) or gas (e.g. in the form of aerosol).

By suitable choice of the sign of the charge of the developing powder or developing liquid a negative or positive print can be obtained at will from any original. If both the printing material and developing powder or developing liquid bear the same charge sign, the powder will only adhere to the discharged areas and a print (positive/ positive) is obtained with the same image value as the original. If the sign of the material and of the developing powder or developing liquid is different, the image values become reversed (negative/positive).

Besides development according to the methods generally known in the electrophotography, also other techniques can successfully be used for instance by applying the method according to the copending patent application Serial No. 856,357, for Development of Electrostatic Latent Images, filed December 1, 1959, and the copending patent application Serial No. 741,017, for Electrophotographic Process, filed June 10, 1958.

If a colored powder was used for making visible the latent image, the visible image obtained can, if necessary, be fixed according to one of the methods known in electrophotography, e.g. by heating, or it can be transferred onto another support, for instance according to the method described in the British Patent 658,699 (Canadian Patent 518,430) and fixed thereon.

Evidently, the present invention is by nomeans limited to one or the other particular embodiment as regards the use of the new electrophotographic materials, and the exposure technique, the charging method, the transfer (if any), the developing method, and the fixing method as well as the materials used in these methods can be adapted to the necessities.

Electrophotographic materials according to the present invention can be applied in reproducing techniques wherein different kinds of radiations, electromagnetic radiations as well as nuclear radiations are used. For this reason, it should be pointed out that although the invention is mainly intended for being applied in connection with methods comprising an exposure, the term electrophotography wherever appearing in the description and the claims, must be broadly understood and comprises both xerography and xeroradiography.

The following examples illustrate the invention without limiting, however, the scope thereof.

Example 1 A photographic baryta paper is coated with a layer from the following solution:

The dried layer has a thickness of 8 This material I is charged with a negative corona and exposed through a '8 diapositive for 8 see. with a 100 watt lamp at a distance of cm. The material is then developed with a developing powder which is obtained 'by mixing together 70 g. of

pitch and 30 g. of carbon black, pulverizing it in a ball mill and mixing 7 parts thereof with 100 parts of iron filing. A true copy of the original is obtained. By using other suitable developing powders iia. those described in V e the U.S. Patents 2,659,670 and 2,753,308, similar good results can be attained.

Example 2 Photographic baryta paper is coated with 10% polyvinyl butyral resin solution in a mixture of equal parts of ethanol and acetone. The dried layer has a thickness of 4 On this layer is coated a solution of 40 .C., obtained by dissolving whilst heating 10 g. of the compound 18 of the table in 100 cm. of dimethylfoirnamide and adding 10 mg. of 3,3'-diethyl-thiacarbocyanine iodide thereto. After rapid drying with an air current of 40 C., the formed layer has a thickness of 6 The material is further treated as in Example 1 but exposed for only 5 sec. After development and fixation as in Example 1, a true copy of the original is obtained.

Example 3 Paper of 90 g./sq. m. covered with an aluminum sheet of a thickness of 12 1. is coated With a layer from the following solution:

Acrylic acid ester polymer g 5 Ethylacetate -i cm. 20 Methylene chloride crn. 40 Compound 4 of the table g 5 Bleu Kiton A (CI. 42052) mg 10 Dimethylformamide cm. 40

Example 4 Baryt-a paper is impregnated with a solution consisting of 10 cm. of glycerine, cm. of ethanol and 45 cm. of water. The excess of water is rcmovedand the paper A is dried. Hereto is applied a second layer coated from a solution of the following composition:

Vinylchloride copolymer g Acetone cm. Compound 14 of the table g 4 Fuchsine (CI. 42510) a mg 8 Dirnethyli'ormamide crn. 50

The dried layer has a thickness of 7;/.. The paper obtained is then electrostatically charged and exposed through a diapositive during 17 sec. Ai-terdevelopment and fixation as in Example 1, a true copy of the original is obtained.

Example 5 Paper of g./ sq. m. covered with an aluminum sheet of 8 thickness is coated with a layer from the following solution: 7

Vinyl acetate resin g 5 Acetone cm. 50 Compound 3 of the table g 5 Crystal Violet (CI; 42555) mg 12 Dimethylformamide crn. 50

The dried layer has a thickness of 7 The paper obtained is then negatively charged and exposed for 20 sec. through a line original. After development and fixation as in Example 1, a true copy of the original is obtained.

Example 6 Baryta paper is coated with a layer from the following solution:

Copolymer of vinyl chloride and vinyl acetate g Methylene chloride c1n. 50 Fuchsine (CI. 42510) mg 8 Compoiuid 11 of the table g 5 Dimethylformamide cm. 50

The dried layer has a thickness of 8,u. The material is electrostatically charged and exposed for 5 sec. accord-- A paper of SOg/sq. In. is first coated with a layer from an aqueous solution containing 5% of gelatin and 1.5% of glycerin. After drying a second layer is applied to the treated paper. This second layer is made from a solution prepared by dissolving 80 g. of poly-acrylic acid ester in a mixture of 600 cm. of acetone and 400 0111. of methylene chloride and adding thereto, whilst heating, 80 g. of the compound 5 of the table and 100 mg. of Orange Astrazon G (CI. 48035). Next, this material is rapidly dried with warm air. This second layer has a thiclmess of 101.6. After electrostatically charging the material obtained, it is exposed through a diapositive for 5 seconds with a 100 watt lamp at a distance of cm. After development and fixation as in Example 1, a true copy of the original is obtained.

Example 8 A paper of Wood fibers of 70 g./ sq. m. is impregnated with a 3% aqueous solution of a cationic organic nitrogen antistatic agent. After drying, one side of this treated paper is coated with a thin layer from a solution of 90 g. of a polyvinyl acetate resin in 1 litre of methylene chloride. The dried layer has a thickness of 4 Next, is applied a second layer from a solution obtained by dissolving 50 g. of the compound 18 of the table and 40 mg. of l,1-diethyl-2,2'-cyanine iodide in a mixture of 500 cm. of dimethylformamide and 500 cm. of acetone. The material is quickly dried with a warm air current. The thickness of this second layer amounts to 71.0. This material is negatively charged and next exposed for 3 sec. through a diapositive with a 100 watt lamp at a distance of 10 cm. Thereafter the material is developed with a mixture of 100 parts of iron filing and 5 parts of a xerographic developing dye and fixed by heating. A clear and sharp copy of the original is obtained.

Example 9 A baryta composition usual for photographic paper, consisting of 1 part by weight of gelatin, 9 parts by weight of barium sulphate, /2 part by weight of a trimethyl alkyl ammonium chloride antistatic agent and 18 parts by weight of water are applied to paper with an air knife and dried. The paper provided with this layer is then calendered. Hereafter is applied to this treated paper a second 10 layer from a solution of 5 g. of a butyraldehyde acetate of polyvinyl alcohol in cm. of methylene chloride and 20 cm. of butylacetate wherein 5 g. of compound 12 of the table and 10 mg. of Bleu Zapon Solide 3 G (CI. 51005) were dispersed. After drying, this second layer has a thickness of 8,11 The material obtained is then electrostatically charged and exposed through a diapositive for 3 seconds with a watt lamp at 10 cm. distance. After development and fixation as in Example 1, a true copy of the original is obtained.

Example 10 An unbrushed and cleaned aluminum sheet is coated with a layer from the following solution:

After careful drying the layer has a thickness of 9 a. After negatively charging the material obtained, it is exposed through a diapositive for 0.6 second with a 100 watt lamp at a distance of 10 cm. The latent image formed is developed with a mixture of 100 g. of glass beads and 5 g. of a xerographic developing dye and fixed by heating. The exposed parts of the light-sensitive layer can now be washed away with dioxane or with methylglycol acetate. After shortly wetting the relief image obtained with a 1.5% solution of sodium hydroxide, a printing plate is obtained which is ready for being tightened on the offset machine. The fixed powder image immediately adsorbs ink and the prints manufactured are sharp and strong.

We claim:

An electrophotographic copying process which comprises exposing an electrostatically charged photoconductive insulating layer comprising p,p'-dibenzoyl aminostilbene to a light image whereby the light struck area is discharged and developing said image of electrostatic charges with an electroscopic material.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,691 Carlson Oct. 6, 1942 2,663,636 Middleton Dec. 22, 1953 2,997,387 Tanenbaum Aug. 22, 1961 3,005,707 Kallman et al Oct. 24, 1961 FOREIGN PATENTS 562,336 Belgium May 13, 1958 1,177,936 France Dec. 8, 1958 580,075 Canada July 21, 1959 110,513 Germany Apr. 27, 1961 OTHER REFERENCES Hannay: Semiconductors, pp. 634-649 and 652-675, Reinhold (1959) pages 650-651 cited in the last Otfice action; pages 634-645 and 650-651 principally relied on herein.

Kallman et al.: Physical Review, vol. 97, No. 6, March 15,1955, pages 1596-1610.

Hannay: Semiconductors, pages 650-651 (1958).

Drefahl et al.: Naturwissenschaften 42, 624 (1955). 

